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The Nano-Spintronics-Cluster-Tool

PGI-6 is permanently developing dedicated methods and up-to-date instrumentation in spectroscopy, microscopy and spectromicroscopy to enable and perform leading edge research.

Nano-Spintronics-Cluster-Tool

The Nano-Spintronics-Cluster-Tool is a dedicated experimental platform for magnetism- and spintronics-related activities in our institute and integrates various complementary methods into a single instrument within an ultrahigh vacuum environment (UHV).

A central part of the Nano-Spintronics-Cluster-Tool is a high-resolution scanning electron microscope (SEM). The spatial resolution limit at high beam energies (30 keV) is 3 nm, while a beam booster improves the resolution at low beam energies (down to 0.1 keV). A high beam current of up to 5 nA in combination with an electron spin polarization detector allows fast structural and magnetic studies (SEMPA) on the mesoscale at variable temperatures (700 down to 30 K).

Figure: Top view of the Nano-Spintronics-Cluster-Tool: The left chamber houses the SEM, the spin polarization detector, and the FIB. The chamber on the right side contains the low temperature STM in the front part and the preparation and analysis chamber in the back. A transfer chamber (middle) connects the two units and enables in-situ access to all attached preparation and characterization tools without vacuum break.

Magnetic contrast with SP-STM

We tested the performance of the STM and the ability to achieve spin contrast by investigating thin (1–2 ML) Fe films on W(110), the standard test system for SP-STM [O. Pietzsch et al., Phys. Rev. Lett. 84, 5212 (2000)]. An in-situ grown Fe wedge is studied in an area, where the Fe film is 1.5 ML thick and thus exhibits areas with one or two ML Fe coverage, respectively. We used a wet chemically etched tip made of antiferromagnetic bulk Cr. The figure shows the simultaneously acquired topography (a) and differential conductivity (dI/dV) map at E-EF=-300 meV (b) as well as a 3D representation of the topography colored according to the spectroscopic data (c). The experiment was performed at 4.8 K.

The topography image (a) was measured in the constant-current mode with a gap voltage of -300 mV addressing occupied states and a tunneling current of 2.5 nA. The scan area (180 nm x 180 nm) comprises 3 surface steps of the W(110) substrate and spans a total height difference of about 0.8 nm including the islands on the topmost terrace. The post-annealing treatment at 560 K causes the Fe atoms in the second ML to diffuse to the step edges, where 2 ML high Fe stripes are formed [red marks in (c)]. Dislocation lines in the 2 ML areas [red arrow in (a)] run along the [001] direction. The simultaneously recorded dI/dV map at E-EF=-300 meV in (b) displays strong contrast in the 2 ML areas only. The dislocation lines appear as bright lines running along [001]. The alternating brown/yellow contrast is due to magnetic domains of the out-of-plane magnetized 2 ML-thick Fe film. The first Fe ML on W(110) is in-plane magnetized and does not contribute to the magnetic contrast of this image. The conductivity map was measured by lock-in detection at a frequency of 2700 Hz and a peak-to-peak modulation amplitude of 42 mV. The overlay of topography and dI/dV map in (c) gives a visual impression of the subtle nanoscale structure-magnetism correlation.